<?php
abstract class Lesson{
	private $duration;
	private $costStrategy;

	function __construct($duration,CostStrategy $strategy){
		$this->duration = $duration;
		$this->costStrategy = $strategy;
	}


	function cost(){
		return $this->costStrategy->cost($this);
	}

	function chargeType(){
		return $this->costStrategy->chargeType();
	}

	function getDuration(){
		return $this->duration;
	}

}